A known coil spring forming apparatus comprises, for example, a core bar and a lead screw provided in parallel with the core bar. The lead screw of the coil spring forming apparatus has a spiral groove that is formed so as to correspond to a pitch and a pitch angle of a coil spring that is to be formed. In the above coil spring forming apparatus, the core bar and the lead screw are rotated, the wire material is guided on the core bar by the spiral groove of the lead screw, and the wire material is wound round the core bar in a predetermined pitch and a pitch angle to manufacture a coil spring.
However, the above coil spring forming apparatus involves various problems such as requiring laborious work to design and fabricate the lead screw, lacking general applicability, i.e., being capable of forming only a coil spring having a pitch and a pitch angle corresponding to the spiral groove of the lead screw, and it being very difficult to produce coil springs having a pitch or a pitch angle changing greatly at a midway point.
Consequently, a coil winding machine employing a pulley-like guide in place of the above lead screw has been developed. The coil winding machine has a core bar and a pulley-like guide arranged at a position separated away from the core bar in the radial direction thereof, and the pulley-like guide moves along the axial direction of the core bar at a predetermined speed. The wire material is wound round the core bar while being guided by the pulley-like guide. Here, the pitch and the pitch angle of the coil spring that is to be obtained is controlled by controlling the moving speed of the pulley-like guide.
In the above coil winding machine, however, the pulley-like guide is disposed at a position separated away from the core bar, and the wire material is not directly guided onto the core bar. Therefore, while estimating the pitch and the pitch angle of the wire material that is actually wound on the core bar, the motion of the pulley-like guide must be controlled in accordance with the estimated pitch and pitch angle.
Therefore, laborious work is required for preparing input data for controlling the pulley-like guide and, furthermore, the pitch of the obtained coil spring varies. Further, since the pulley-like guide and the core bar are separated away from each other, it is not possible to directly control the motion of the wire material on the core bar. When attempting to form a coil spring having a pitch that sharply varies, therefore, it is difficult to have the motion of the guide follow the change in the pitch. When attempting to forcibly move the guide so as to follow the change in the pitch, the wire material slips on the core bar, causing variation in the pitch.
In order to solve the problems of the above coil winding machine, there has been proposed a coil winding machine comprising a core bar, a core bar drive mechanism, a chuck for gripping an end of a wire material so as to fix it on the core bar, a guide member arranged in parallel with the core bar, a moving head being held by the guide member so as to move in a direction parallel with the core bar, a first holder being provided on the moving head so as to move reciprocally toward or away from the core bar and to rotate around an axis which extends in the radial direction of the core bar, a guide drive mechanism reciprocally driving the first holder toward or away from the core bar, a first guide being provided on the first holder and having a groove portion that fits the material of a coil spring, an axial drive mechanism driving the moving head so that the first guide moves in the axial direction of the core bar in accordance with the pitch of the coil spring at a speed corresponding to the rotational speed of the core bar, a second holder turning together with the first holder, a second guide being provided on the second holder, coming in rotational contact with the material so as to prevent the material from detaching, and feeding the material toward the first guide, and an angle-varying actuator controlling the direction of the holder to direct the first guide and the second guide so that the first guide and the second guide interlock and face a direction corresponding to a pitch angle of the coil spring (patent document 1).    [Patent document 1] JP-B-2-33460